a) Field of the Invention
The present invention relates to apparatus and method for monitoring revolution speed values detected by means of revolution speed sensors to be used to control at least gear shift ratio of a continuously variable transmission for a vehicle to determine whether at least one of the revolution speed sensors has failed. The revolution speed sensors include an engine revolution speed sensor and a drive axle (input) and driven axle (output) revolution speed sensors of the continuously variable transmission.
b) Description of the Related Art
A Japanese Patent Application First Publication No. Heisei 7-317894 published on Dec. 8, 1995 exemplifies a previously proposed gear-shift-ratio-and-lock-up control apparatus for a continuously variable transmission in a vehicle.
In the previously proposed gear-shift-ratio-and-lock-up control apparatus disclosed in the above-identified Japanese Patent Application First Publication, the gear shift ratio and lock-up controls are advanced on the basis of detected values of an engine revolution speed, an input axle (turbine axle of a fluid coupling device) revolution speed of the continuously variable transmission, an output axle revolution speed (vehicle speed) of the continuously variable transmission, an opening angle of an engine throttle valve, a shift position selection switch, a brake signal, and a longitudinal (vehicular forward/backward) acceleration, and so forth.
It is noted that in the above-described previously proposed gear-shift-ratio-and-lock-up control apparatus, the gear shift ratio and lock-up control using a stepping motor and a lock-up clutch are carried out on the basis of read values of the revolution speed of the engine output axle, the input axle (turbine axle) and output axle (vehicle speed) of the continuously variable transmission from the corresponding revolution speed sensors with detected values of the revolution speed sensors being deemed to be correct.